The molding of thermoset polymers is a technologically and commercially important processing technique. In one known version of this technique, a liquid cyclic olefin monomer resin is combined with at least one metal carbene olefin metathesis catalyst to form a ROMP composition, and the ROMP composition is added (e.g., poured, cast, infused, injected, etc.) into a mold. The ROMP composition is subjected to conditions effective to polymerize the ROMP composition and on completion the molded article is subjected to any optional post cure processing that may be required. As is known in the art, the liquid cyclic olefin monomer resin may optionally contain added modifiers, fillers, reinforcements, flame retardants, pigments, etc. Examples of such prior art ROMP compositions are disclosed in U.S. Pat. Nos. 5,342,909; 6,310,121; 6,515,084; 6,525,125; 6,759,537; 7,329,758, etc.
Commercially important cyclic olefin monomer resins generally comprise readily available and inexpensive cyclic olefins such as norbornene monomers, particularly dicyclopentadiene (DCPD). Unfortunately, high purity DCPD melts at 32° C.-34° C. and is thus a solid at room temperature (typically 20-25° C.). Therefore, high purity DCPD must be heated during its formulation with catalyst(s) and other additives, and transported through heat-jacketed lines to maintain a liquid state for use in many polymer molding techniques such as RIM (Reaction Injection Molding), RTM (Resin Transfer Molding), and VARTM (Vacuum Assisted Resin Transfer Molding).
It is known in the art that the melting point of DCPD can be depressed by adding an adulterant in the form of higher cyclopentadiene oligomers that are copolymerizable with dicyclopentadiene such as trimer of cyclopentadiene (tricyclopentadiene). In fact, commercially available liquid DCPD monomer resins for use in molding of polymer articles typically contain between 10%-30% by weight of tricyclopentadiene, and lesser amounts of higher oligomers of cyclopentadiene such as tetramers and pentamers of cyclopentadiene (e.g., tetracyclopentadiene and pentacyclopentadiene).
Liquid DCPD monomer resins for use in molding polymer articles containing higher amounts of cyclopentadiene trimer have been reported in the literature. European Pat. No. EP0271007B2 and U.S. Pat. No. 4,703,098 disclosed liquid mixtures containing (a) 52% by weight DCPD, 43.25% by weight tricyclopentadiene, and 4.75% by weight tetracyclopentadiene; and (b) 42% by weight DCPD, 51.5% by weight tricyclopentadiene, 6.5% by weight tetracyclopentadiene. However, the inventors have discovered that below 40° C., particularly at or below room temperature, solids precipitate out of such mixtures. This is particularly problematic as below 40° C., particularly at or below room temperature such prior art resin compositions are not suitable for use in preparing composite articles, particularly using resin infusion techniques, such as VARTM, as the solids may clog the infusion ports and/or equipment and may also act to reduce infusion of the resin into the composite substrate material. Furthermore, these solids may also act to clog or foul equipment such as material supply lines and/or injection ports utilized in reaction injection molding (RIM) techniques, when molding polymer articles and/or polymer composite articles.
To successfully mold a polymer article and/or polymer composite article using liquid DCPD monomer resins, it is important that the molded article be free or substantially free of defects (e.g., unwanted pores, cavities, bubbles, voids, knit lines and/or internal stress fractures). This issue is particularly important as molded polymer articles and/or polymer composite articles possessing defects will either require repair or need to be discarded, which in either situation leads to increased manufacturing costs.
In a typical molding operation the temperature of the pre-catalyzed liquid DCPD monomer resin is typically below 40° C., and preferentially at or below room temperature. Heating the pre-catalyzed liquid DCPD monomer resin above room temperature, particularly above 40° C., generally reduces the pot life of the ROMP composition (catalyzed monomer resin), making it difficult to adequately fill the mold and/or infuse the substrate materials, particularly when making large polymer articles and/or large polymer composite articles. In addition, heating of the liquid DCPD monomer resin may require special equipment (e.g., heated tanks and/or lines) which adds to the overall cost of molding ROMP polymer articles and/or ROMP polymer composite articles. Methods and additives for controlling the pot life of catalyzed liquid cyclic olefin monomer resins (e.g., liquid DCPD monomer resins) are known; however, generally at temperatures above 40° C. large amounts of additives may be required to provide adequate pot life, but the use of large amounts of such additives may detrimentally affect the thermal and mechanical properties of the molded polymer article and/or polymer composite article, thereby requiring the need for additional optional post cure processing which also increases the overall cost of molding ROMP polymer articles and/or ROMP polymer composite articles.
Typically, following catalyzation of the liquid DCPD monomer resin to form a ROMP composition, the polymerization of the monomer resin progresses and the viscosity of the ROMP composition increases, progressing from a liquid state, through a gel state, to the final hard polymer. At some point during the progression, the temperature generally begins to increase rapidly leading to a sharp exotherm. A general issue with molding polymer articles using liquid DCPD monomer resins is that during the exotherm phase of the polymerization cycle volatilization of dicyclopentadiene and/or other low boiling compounds which may be present in the liquid DCPD monomer resin (e.g., cyclopentadiene monomer) often lead to the formation of defects in the interior and/or on the surface of the molded polymer article and/or polymer composite article. It is known in the art that low molecular weight, low boiling hydrocarbon compounds (e.g., cyclopentadiene monomer) can be removed from liquid DCPD monomer resin by vacuum stripping and/or inert gas sparging. However, the inventors have discovered that removal of low molecular weight, low boiling hydrocarbon compounds such as cyclopentadiene monomer alone is not sufficient to reduce and/or eliminate defect formation in the interior and/or on the surface of molded ROMP polymer articles and/or ROMP polymer composite articles.
While there have been attempts to modulate the exotherm temperature (e.g., through manipulation of the mold temperature and/or addition of additives) to control defect formation, it is typically advantageous to allow the ROMP composition to achieve a maximum (high) exotherm temperature so as to optimize the thermal and mechanical properties of the molded polymer article and/or polymer composite article, thereby reducing and/or eliminating the need for additional optional post cure processing.
Therefore, it would be useful and commercially important to be able to rapidly heat the ROMP composition in a mold (e.g., at a rate greater than 0.5° C./min) and/or add the ROMP composition to a mold preheated at a temperature of about 60° C. to 200° C., either of which would allow the ROMP composition to achieve a maximum (high) exotherm temperature and additionally allow for a reduction in overall cycle time. This reduction in cycle time provides for an economic advantage in that more polymer articles and/or polymer composite articles can be made during the same time period. In other words, it would be preferable to be able to add the ROMP composition to a heated mold and/or begin heating the ROMP composition as soon as possible once the mold is filled and/or the composite substrate material is infused with the ROMP composition. More particularly, it would be preferable to be able to add a ROMP composition, having an initial temperature below 40° C., preferably at or below room temperature, to a mold heated at 60° C. to 200° C. and/or begin heating the ROMP composition in the mold at a rate greater than 0.5° C./min as soon as the mold is filled and/or the composite substrate material is infused with the ROMP composition.
Generally, however, it has been observed that if liquid DCPD monomer resin compositions, containing 10%-30% cyclopentadiene trimer are utilized in a ROMP composition to mold polymer articles and/or polymer composite articles, the resultant molded polymer article and/or polymer composite article will typically contain defects, particularly if such a ROMP composition at an initial temperature below 40° C., preferably at or below room temperature, is added to a mold preheated at a temperature of about 60° C. to 200° C. and/or if the mold is rapidly heated at a rate greater than 0.5° C./min.
Therefore, despite the advances achieved in the art, there is a need for liquid cyclic olefin monomer resins, particularly resins which are storage stable homogenous liquids, which can be combined with a catalyst composition comprising at least one metal carbene olefin metathesis catalyst to form a ROMP composition, where the ROMP composition may be added to a preheated mold and/or the mold may be rapidly heated to prepare molded polymer articles and/or polymer composite articles, where the resultant molded polymer articles and/or polymer composite articles are free or substantially free of defects.
More particularly, there is a need for liquid DCPD resin compositions that are stable homogenous liquids between 39° C. to 10° C., which can be combined with a catalyst composition comprising at least one metal carbene olefin metathesis catalyst to form a ROMP composition, where the ROMP composition is below 40° C., preferably at or below room temperature, and the ROMP composition may be added to a mold preheated to 60° C. to 200° C. and/or the mold may be rapidly heated (e.g., at a rate greater than 0.5° C./min) to prepare molded polymer articles and/or polymer composite articles, where the resultant molded polymer articles and/or polymer composite articles are free or substantially free of defects.
The present invention is directed to addressing one or more the aforementioned concerns.